That sounds a lot like asking how to bring more Catholics to the Vatican. Nevertheless, it's fun to note that the responses are arguing over how little a "liberal" speaker could take for a speech. That is, they are discussing how that person should take the time to travel to Chapel Hill to give a speech for a pittance as opposed to other uses of his time. One finds a large speaker's fee "disgusting"; another says that the "bozo" liberal who required a huge speaking fee "would be putting money ahead of taking some personal responsibility for stopping our impending societal train wreck." Others try to reason to the True Price of "progressive speakers."

Apparently, even "prominent liberals" understand free-market principles and opportunity costs when it comes to their own capital — in this case, their time, speaking ability, ideas and celebrity — and have a revealed preference not to give those things freely to their fellow-travelers in Chapel Hill who apparently feel entitled to them ("From each according to their means, to each ..." ad nauseam).